Traumatic brain injury (TBI) is the leading cause of mortality in children over one year of age. Evidence suggests that hypotension after initial brain injury contributes to secondary brain injury and worsens outcome. Altered cerebral physiology including impaired cerebral autoregulation and hyperemia may also contribute to poor outcome following pediatric TBI. Therefore, characterizing optimal cerebral hemodynamics immediately following severe pediatric TBI is important. The objective of the proposed research is to describe the relationship between cerebral hemodynamics following severe pediatric TBI and outcome. The specific aims proposed here will provide new information regarding the early cerebral hemodynamic management of children with severe TBI. The aims are to examine (1) the relationship between cerebral perfusion pressure and outcome, (2) the relationship between persistent impairment of cerebral autoregulation and outcome, and (3) the age-related incidence of hyperemia. The investigators will also examine the relationship between hyperemia and impaired cerebral autoregulation and the relationship between persistent hyperemia and outcome following severe pediatric TBI. It is important to conduct these studies in children of various ages because (1) cerebral hemodynamics change significantly during development, (2) optimal cerebral hemodynamics following severe TBI may differ in young children compared to older children, (3) there is a paucity of physiologic data in children, and (4) pediatric practice is currently extrapolated from adult practice. The results and experience gained in this research will aid in the future study of cerebral hemodynamics in children at risk of cerebral ischemia both with and without TBI. The proposed research will be carried out at the University of Washington, well-known known for mentored patient-oriented research.